1. Field of the Invention
The invention generally relates to an internal combustion engine mounted on a vehicle and the like. More particularly, the invention relates to an internal combustion engine preheated upon or before starting, and a control method of the same.
2. Description of Related Art
In recent years, an internal combustion engine mounted on an automobile and the like is required to improve startability upon cold starting, reduce fuel consumption, and improve exhaust emission.
In response to these requirements, a heat-accumulating device for the engine as described in JP-A-6-185359 has been proposed. According to the disclosed heat-accumulating device, a water-cooled internal combustion engine includes a first cooling-water passage running through a cylinder block and a second cooling-water passage running through a cylinder head. A heat accumulator is provided in the second cooling-water passage. When the internal combustion engine is cold, the cooling water heated by the heat accumulator is circulated through the second cooling-water passage so as to allow early completion of warm-up of the water passage so as to allow early completion of warm-up of the intake system and fuel supply system by warming the cylinder head first.
Upon cold starting of the internal combustion engine, the fuel is likely to adhere to the wall surface of, for example, an intake port, a combustion chamber and the like because of the low temperature. Therefore, it is known that, when the internal combustion engine is cold, an air-fuel ratio of the engine is reduced taking into account of the amount of the fuel adhering to the wall surface.
In the conventional heat-accumulating device for the engine as described above, however, the air-fuel ratio of the engine is not taken into account in the case of warm-up of the intake system and fuel supply system using hot cooling water stored in a heat-accumulating container. Therefore, the heat-accumulating device may be controlled to reduce the air-fuel ratio despite the fact that the wall-surface temperature of the intake port or combustion chamber has been increased.
If the air-fuel ratio is reduced at a high temperature of the wall surface of the intake port, combustion chamber and the like, a fuel-rich mixture is produced. As a result, a relatively large amount of unburned fuel components is discharged from the internal combustion engine, thereby possibly degrading the exhaust emission.
It is also known that, at a cold starting of an internal combustion engine having spark plugs, for example, a gasoline engine, an exhaust purifying catalyst is not activated yet. Therefore, the ignition timing is retarded to raise the exhaust temperature such that the exhaust purifying catalyst is activated as early as possible. During the cold starting, however, combustion of the air-fuel mixture is likely to be unstable. In this respect, a degree of retarding the ignition timing is limited.
The conventional heat accumulating device for the engine as described above has not taken into account of the ignition timing set for warming up the intake system and fuel supplying system with the hot cooling water stored in the heat accumulating container. Therefore, the degree of retarding the ignition timing may possibly be limited despite the fact that the ignition performance and combustion stability of the air-fuel mixture have been obtained by warming up the intake system and fuel supplying system.
If the degree of retarding the ignition timing is limited when the ignition performance and combustion stability of the air-fuel mixture have been compensated by warming up the intake system and fuel supply system, the exhaust temperature cannot be raised to a desired value. As a result, it may take a long time to activate the exhaust purifying catalyst.